Motor starting switch



Sept. 22, 1936. s, SVENSON 2,054,957

MOTOR STARTING SWITCH Filed Sept. l1, 1933 INVENTOR. f7/ef? JP3/7.5 0/ 7 A TTORN E YS.

' in general Patented Sept. 22, 1936 UNITED STATES PATENT oI-EicE MOTOR STARTING SWITCH l l Sven Svenrson, San Francisco, Calif. Application September 11, 1933, Serial 190.688.955

' A4. claims. (c1. rzml-so) My invention relates to means for controlling electric circuits and is especially concerned with a switch which is 'responsive to 4rotational or centrifugal force. l

An object of my Ainvention isv to provide an improved electrical switch. A further object of my inventon is to provide an inexpensive and compact switch especially vfor use in starting electric motors.

Another object of my invention is to improve centrifugally-operated electrical switches. l

'Ihe foregoing and other objects are attained in the embodiment oi my invention illustrated in the drawing, in which Figure l is a side elevation of an electric motor, a. Yportion being broken away and showing in cross-section the starting switch of my invention incorporated therein. Figure 2 is a cross-#section the plane of which is indicated by the line 2-'2 of 'Figure 1 with my motor starting switch in its stationary condition. Y Figure 3 is a cross-section the plane of which is indicated by the line 2-2'of Figure 1 but with the motor starting switch of my invention in rotating condition.

In its preferred form, the motor` starting' switch of my invention includes a pair of Telectrically-conducting, mutually-insulatedv mem bers, together providing a chamber and adapted to be rotated, together with la .liquid electrical conductor in the chamber which is adapted to form a thin ring around the inner periphery of the chamber upon rotation thereof, together with an insulating baffle disposedin the chamber and adapted to divide the ring into two portions but adapted to permit the liquid conductor to be undivided when the rotatable members are stationary. A

Although the switch of my invention is susceptible to numerous uses, it is particularly advantageous in conjunction with electric motors for starting purposes. For this reason I have illustrated my switch in such environment. The usual electric motor, generally designated i, includes a stator 1 which is provided with a suitable mounting base 8 supporting electrical coils 9. Located within the stator 1 is a rotor II mounted on a. through-shaft I2 suitably supported in bearings I3 and I4. In the customary operation of such motor, the coils 9 are utilized in starting, but after the rotor II has attained a predetermined speed the coils 9 no longer are necessary and are customarily removed from the electrical circuit. j

,In order toaccomplish this result, I preferably mount on the 'shaft I2-in a convenient location,l a bushing I 6 of insulating material which is pressed onto the shaft I2 or otherwise arranged to rotate therewith. Against a shoulder I1 on the bushing I6is a disc I8 which is preferably formed of'metal. Co-operating with the disc or member I8 is a comparable metal disc I9 likewise mounted onthe bushing IB. In order that the two members I8 and I9, although of electrically conducting material, may be mutually insulated, I preferably arrange them so that they are peripherally spaced apart to provide an annular insulating groove 2|. In addition to such insulation, I preferably dispose between said members I8 and I9 an insulating layer 22 which conveniently is of relatively soft rubber. Further in accordance with my invention, I interpose between the members I8 and I9 and likewise embed in the rubber layer 22, an insulating baille 23 of planar form and annular configuration. The baille 23 is tightly clamped in place and the rubber 22 is slightly deformed therearound in order to provide a tight seal by means of a :lamb-nut 24 which is threaded on the bushingV I9 and clamps thedescribed members between the shoulder- I1 andthe -nut 2l, thus providing a chamber 26 which is liquid and gas tight.

I preferably include the members I8 and I9 in an electrical circuit, and for this reason the member i8, for instance, carries an annular ring 21 which is in electrically-conducting union with the Amember I8 and is adapted to be abutted by a brush 28 carried in a suitable holder 29 and connected in an electrical circuit to the coils 9 by alead 3I. Comparably, the member `I9 carries a conducting ring 32 which is in electrical union .with the member I9 and against which av suitable brush 33 abuts. The brush Vis carried in a suitable holder 3l included in circuit with the coils 9 by a conductor 36. The described circuit is therefore complete except for the gap between the members I8 and I9.

In order that such gap may be suitably bridged, I dispose within the chamber 26 a quantity oi a liquid electrical conductor, such as mercury 31, in such an amount that when the device as a whole is stationary the mercury forms a pool in the bottom oi the chamber 26, as indicated in Figure 2, the dimensions or volume of the pool being such that the mercury or other conductor bridges across the baille 23 and completes the circuit between the conducting members I8 and I9. The quantity of mercury 31. however, is such, or, looked at from another aspect. the height or dimension of the baille 23 is such, that when the shaft I2 is rotated and attains a predetermined speed the mercury 31 is thrown by centrifugal force radially outward to form ia ring 39 on the inner periphery of the chamber 26, so that the mercury is divided into two isolated portions by the baille 23, each portion, however, still being in electrical union with its associated member I8 or I9. Thus, the electrical circuit is broken in the mercury upon- .attainment of a predetermined shaft speed.

Since mercury is relatively heavy and possesses a high inertia, in certain instances I provide a roughened surface 4I on the interior of the chamber 26 in order that the mercury will be impelled to rotate with the members IB and I9 and will be thrown outwardly by centrifugal force into the thin lm or ring 39.

When the shaft I2 drops below a predetermined speed, or becomes stationary, the ring of mercury 39 by gravity drops into a pool 31, as indicated in Figure 2, again bridging the baiile 23 and replacing the coils 9 in circuit for a subsequent start of the motor or for operation members on said shaft forming a chamber therearound and insulated from each other, means yfor including said members in an electric circuit,

an insulatingbaiile dividing said chamber into compartments, and a liquid electrical conductor in said chamber in sufficient quantity to bridge said baille when said shaft is stationary but adapted to be separated by said baie under the inuence of centrifugal force when said shaft is rotating.

2. A motor starting switch comprising a pair of` rotatable electrically conducting mutually in- A sulated members forming a chamber, a liquid electrical conductor in said chamber adapted to form a thin ring o n the inner periphery of said,

chamber under the influence of centrifugal force when said members are rotating, and an insulating baille in said chamber of sulcient size to divide said ring into two parts but of insufficient size to divide said liquid conductor when said members are not rotating.

3. A motor starting switch comprising a rotatable shaft, electrically conducting members on said shaft, mercury when quiescent in contact with said members, and means for dividing said mercury into electrically isolated portions in response to centrifugal force upon rotation of said shaft. f

4. A motor starting switch comprising a rotatable container having mercury therein, electrically conducting members electrically communicating with said mercury, and means effective upon rotation of said container for dividing said mercury into two electrically isolated portions in response to centrifugal force.

SVEN SVENSON. 

